Development of YSZ Thermal Barrier Coatings Using Axial Suspension Plasma Spraying

Abstract

Abstract:The axial injection of the suspension in the atmospheric plasma spraying process (here called axial suspension plasma spraying) is an attractive and advanced thermal spraying technology especially for the deposition of thermal barrier coatings (TBCs). It enables the growth of columnar-like structures and, hence, combines advantages of electron beam-physical vapor deposition (EB-PVD) technology with the considerably cheaper atmospheric plasma spraying (APS). In the first part of this study, the effects of spraying conditions on the microstructure of yttria partially-stabilized zirconia (YSZ) top coats and the deposition efficiency were investigated. YSZ coatings deposited on as-sprayed bond coats with 5 wt % solid content suspension appeared to have nicely-developed columnar structures. Based on the preliminary results, the nicely developed columnar coatings with variations of the stand-off distances and yttria content were subjected to thermal cycling tests in a gas burner rig. In these tests, all columnar structured TBCs showed relatively short lifetimes compared with porous APS coatings. Indentation measurements for Young's modulus and fracture toughness on the columns of the SPS coatings indicated a correlation between mechanical properties and lifetime for the SPS samples. A simplified model is presented which correlates mechanical properties and lifetime of SPS coatings.

A constitutive model for the sintering of suspension plasma‐sprayed thermal barrier coating with vertical cracks

“…The Young's modulus was obtained by the initial slope of the unloading curve in the load‐depth plot. More details can be found elsewhere . Indentations were made on the polished cross‐section and were carefully chosen on the solid structures to avoid the VCs.…”

“…More details can be found elsewhere. 29,30 Indentations were made on the polished cross-section and were carefully chosen on the solid structures to avoid the VCs. Over 15 measurements were conducted to improve the statistics.…”

The Influence of Heat Treatments on the Porosity of Suspension Plasma-Sprayed Yttria-Stabilized Zirconia Coatings

“…APS-sprayed topcoats are known for lower thermal conductivity due to their inherently higher porous nature (Ref 8), whereas the EBPVD topcoats are known for better strain tolerance due to their inherent columnar structure (Ref 9). Suspension plasma spraying (SPS) is a relatively new technique compared to APS and EBPVD which has shown to produce topcoats comprising of both high porosity like APS and columnar structures like EBPVD (Ref [10][11][12][13]. SPS coatings have previously shown good results regarding both lower thermal conductivity due to higher porosity and better strain tolerance due to their columnar structure (Ref 14,15).…”

Thermal cycling performances of multilayered yttria‐stabilized zirconia/gadolinium zirconate thermal barrier coatings

“…Therefore, the SPS was applied to spray GZO layers in present work. However, such columnar SPS TBCs directly deposited on rough bond coat exhibit premature failure during high load thermal cycling . This failure might be related to the porous column gaps deriving from the rough bond coat.…”

“…However, such columnar SPS TBCs directly deposited on rough bond coat exhibit premature failure during high load thermal cycling. 28 This failure might be related to the porous column gaps deriving from the rough bond coat. Even with high strain tolerance, these column gaps at the vicinity area of bond coat might facilitate crack propagation during cycling leading to premature failure of TBCs.…”